Method for transmitting and receiving control information through pdcch

ABSTRACT

A method for efficiently transmitting and receiving control information through a Physical Downlink Control Channel (PDCCH) is provided. When a User Equipment (UE) receives control information through a PDCCH, the received control information is set to be decoded in units of search spaces, each having a specific start position in the specific subframe. Here, a modulo operation according to a predetermined first constant value (D) is performed on an input value to calculate a first result value, and a modulo operation according to a predetermined first variable value (C) corresponding to the number of candidate start positions that can be used as the specific start position is performed on the calculated first result value to calculate a second result value and an index position corresponding to the second result value is used as the specific start position. Transmitting control information in this manner enables a plurality of UEs to efficiently receive PDCCHs without collisions.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of the Korean Patent Application No.10-2008-0068633, filed on Jul. 15, 2008, which is hereby incorporated byreference as if fully set forth herein. This application also claims thebenefit of U.S. Provisional Application Ser. Nos. 61/029,576, filed onFeb. 19, 2008 and 61/037,000, filed on March 17, the contents of whichare hereby incorporated by reference herein in their entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to mobile communication technologies, andmore particularly, to a method for efficiently transmitting andreceiving control information through a Physical Downlink ControlChannel (PDCCH).

2. Discussion of the Related Art

The following description can be applied to various mobile communicationmethods. However, a description will be given, particularly withreference to Third Generation Partnership Project Long Term Evolution(3GPP LTE) technologies.

3GPP LTE is a project for improving the UMTS mobile station standard tocope with future technology development in the Third GenerationPartnership Project (3GPP). 3GPP LTE has evolved to Release 8 which isan improved version of the 3GPP standard.

In the 3GPP LTE communication system, various channels are defined foruplink and downlink in the physical layer used in actual signaltransmission. For example, a Physical Uplink Shared Channel (PUSCH), aPhysical Uplink Control Channel (PUCCH), and a Physical Random AccessChannel (PRACH) are defined as uplink physical channels, and a PhysicalDownlink Shared Channel (PDSCH), a Physical Multicast Channel (PMCH), aPhysical Broadcast Channel (PBCH), a Physical Control Format IndicatorChannel (PCFICH), a Physical Downlink Control Channel (PDCCH), and aPhysical Hybrid ARQ (HARQ) Indicator Channel (PHICH) are defined asdownlink physical channels. In the following description, the word“physical” will be omitted for ease of explanation unless the omissioncauses confusing.

Among the various channels, the PDCCH serves to transmit schedulingallocation control information and other control information. In acellular communication system in which one base station (or Node-B)controls a plurality of User Equipments (UEs) or (mobile stations),multiple UEs can receive control information through a PDCCH transmittedfrom the base station. Here, since there is a limit to the number ofPDCCHs that the base station can transmit at once, the base station doesnot previously allocate different PDCCHs to each UE but transmitscontrol information through an arbitrary PDCCH to an arbitrary UE ateach time. Thus, the UE determines whether or not control informationreceived through the PDCCH belongs to the UE based on a UE identifierincluded in the PDCCH. At each time, the UE performs decoding on each ofa plurality of PDCCHs (for a plurality of possible PDCCH formats) andreceives, when it is determined that the PDCCH corresponds to the UE,control information included in the PDCCH and operates according to thecontrol information.

However, the number of combinations of PDCCH regions for transmission ofcontrol information may be great. Excessive UE processing performancemay be required for the UE to decode all PDCCH regions. Accordingly,there is a need to limit PDCCH regions to be decoded by each UE toreduce the number of times the UE performs decoding and thus to reducepower consumption of the UE.

SUMMARY OF THE INVENTION

An object of the present invention devised to solve the problem lies inproviding a technology for efficiently transmitting and receivingcontrol information through a Physical Downlink Control Channel (PDCCH).

Another object of the present invention devised to solve the problemlies in providing a technology for efficiently setting a different startposition of a search space for each UE in order to transmit and receivecontrol information to and from each UE through a different searchspace.

The object of the present invention can be achieved by providing amethod for a User Equipment (UE) to receive control information througha Physical Downlink Control Channel (PDCCH), the method includingreceiving control information from a base station through a PDCCH inunits of Control Channel Element (CCE) aggregations, each including atleast one CCE in a control region of a specific subframe; and decodingthe received control information in units of search space in thespecific subframe, wherein a modulo operation according to apredetermined first constant value (D) is performed on an input value tocalculate a first result value, and a modulo operation according to apredetermined first variable value (C) defined by the equation of

C=floor(N _(CCE) /L _(CCE))

is performed on a value corresponds to the calculated first result valueto calculate a second result value and the search space starts with anindex position corresponding to the second result value (where N_(CCE)represents the total number of CCEs in the specific subframe, andL_(CCE) is the number of CCEs included in the CCE aggregation, andfloor(x) is a largest integer that is equal to or less than x).

In another aspect of the present invention, provided herein is a methodfor a base station to transmit control information through a PhysicalDownlink Control Channel (PDCCH), the method including transmittingcontrol information for a specific User Equipment (UE) through a PDCCHin units of Control Channel Element (CCE) aggregations, each includingat least one CCE in a control region of a specific subframe, wherein thecontrol information for the specific UE is transmitted in units ofsearch space in the specific subframe, and wherein a modulo operationaccording to a predetermined first constant value (D) is performed on aninput value to calculate a first result value, and a modulo operationaccording to a predetermined first variable value (C) defined by theequation of

C=floor(N _(CCE) /L _(CCE))

is performed on a value corresponds to the calculated first result valueto calculate a second result value and the search space starts with anindex position corresponding to the second result value.

In the above methods, preferably, the first constant value (D) ispredetermined to be higher than the first variable value (C).

In addition, it may be advantageous that the input value for a “k+1”thsubframe is set to correspond to the first result value for a “k”thsubframe, where “k” is a non-negative integer.

On the other hand, in the above methods, an identification informationvalue of the UE may be used for the input value for a 1st subframe.

In addition, the first result value may be calculated by multiplying theinput value by a predetermined second constant value (A), adding apredetermined third constant value (B), which result in a intermediatevalue, and performing the modulo operation according to the firstconstant value (D) on the intermediate value.

In this case, preferably, the first constant value (D), the secondconstant value (A), and the third constant value (B) are 65537, 39827,and 0, respectively.

In an embodiment of the present invention, when the specific subframe isthe “k”th subframe, the first constant value is “D”, and the firstconstant value is “C”, the search space starts with a specific startposition Z_(k) in the “k”th subframe, the specific start position Z_(k)in the “k”th subframe is set as an index position corresponding to avalue determined by Z_(k)=[(A·y_(k)+B)mod D] mod C andy_(k)=(A·y_(k−1)+B)mod D, where A and B denote predetermined constantvalues and “k” denotes a subframe index.

In this case, the first constant value “D” may be 65537, and thepredetermined constant values “A” and “B” may be 39827 and 0,respectively.

Here, the index position corresponding to the determined value maycorrespond to a start position of a CCE aggregation corresponding to thedetermined value under the assumption that indices are assigned on a CCEaggregation basis. According to the embodiments of the present inventiondescribed above, it is possible to efficiently transmit and receivecontrol information through a Physical Downlink Control Channel (PDCCH).

Specifically, a different start position of a search space can be setfor each UE so that control information can be transmitted and receivedto and from each UE through a different search space.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification, illustrate embodiments of the invention andtogether with the description serve to explain the principles of theinvention.

In the drawings:

FIG. 1 illustrates an example of a CCE aggregation through which onePDCCH can be transmitted.

FIG. 2 illustrates all possible decoding regions that the UE needs toattempt to decode taking into consideration the CCE aggregation level.

FIG. 3 illustrates an example wherein two different UEs have differentdecoding regions under a specific CCE aggregation level condition.

FIG. 4 illustrates the principle of a generator that generatesidentification dependent randomization numbers according to anembodiment of the present invention.

FIGS. 5 and 6 illustrate an example wherein a part of a binary sequencegenerated by the generator is selected as an initial value according toan embodiment of the present invention.

FIG. 7 illustrates a frame structure in the 3GPP LTE system forexplaining an example in which a communication system operates atregular intervals

FIGS. 8 and 9 illustrate a method for creating an initial value used togenerate a start position of a PDCCH search space using a UE ID and asubframe number according to an embodiment of the present invention.

FIG. 10 illustrates an example wherein one of two UEs having differentCCE aggregation levels fails to receive a PDCCH destined for the UE dueto a PDCCH destined for the other UE.

FIGS. 11 and 12 illustrate examples where a UE ID, a subframe number,and a CCE aggregation level are used to create an initial valueaccording to an embodiment of the present invention.

FIGS. 13 and 14 illustrate examples where an initial value used tocalculate a start position of a PDCCH search space is created using a UEID and a CCE aggregation level according to an embodiment of the presentinvention.

FIG. 15 illustrates the concept of the number of hits used fordetermining performance when parameter values are calculated accordingto an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Reference will now be made in detail to the preferred embodiments of thepresent invention with reference to the accompanying drawings. Thedetailed description, which will be given below with reference to theaccompanying drawings, is intended to explain exemplary embodiments ofthe present invention, rather than to show the only embodiments that canbe implemented according to the invention. The following detaileddescription includes specific details in order to provide a thoroughunderstanding of the present invention. However, it will be apparent tothose skilled in the art that the present invention may be practicedwithout such specific details.

In some instances, known structures and devices are omitted or are shownin block diagram form, focusing on important features of the structuresand devices, so as not to obscure the concept of the present invention.The same reference numbers will be used throughout this specification torefer to the same or like parts.

When a UE decodes all PDCCH regions, the complexity of the UE andbattery consumption are increased. Therefore, it is necessary to specifya PDCCH decoding region for each UE. To accomplish this, there is a needto study in more detail a resource space through which the PDCCH istransmitted.

A PDCCH can be transmitted through a CCE aggregation including one ormore Control Channel Elements (CCEs). In addition, a plurality of PDCCHscan be transmitted in one subframe. Here, the term “CCE” refers to aresource unit for transmission of control information, which is a unitcorresponding to a specific number of resource elements in the resourcespace. A detailed description of the concept of the CCE is omittedherein since it is apparent to those skilled in the art.

PDCCH formats can be classified as follows according to the size of aCCE aggregation used for PDCCH transmission as described above.

TABLE 1 PDCCH format Number of CCEs 0 1 1 2 2 4 3 8

FIG. 1 illustrates an example of a CCE aggregation through which onePDCCH can be transmitted.

The term “Total Number of CCEs” in FIG. 1 refers to the number of CCEsincluded in one subframe. However, the number of CCEs included in onesubframe may vary according to system requirements. In FIG. 1, areference numeral “100” denotes a format (PDCCH format 1 in Table 1) inwhich one PDCCH is transmitted through one CCE, a reference numeral“200” denotes a format (PDCCH format 2 in Table 1) in which one PDCCH istransmitted through 2 CCEs, a reference numeral “300” denotes a format(PDCCH format 3 in Table 1) in which one PDCCH is transmitted through 4CCEs, and a reference numeral “400” denotes a format (PDCCH format 4 inTable 1) in which one PDCCH is transmitted through 8 CCEs.

That is, as shown in FIG. 1, the size of a CCE aggregation used totransmit one PDCCH may vary depending on channel environments of each UEas shown in FIG. 1. In the following description, the number of CCEsused to transmit one PDCCH will be referred to as a “CCE aggregationlevel”. Thus, when each UE decodes a PDCCH, the UE must determine thesize of a decoding region for each CCE aggregation level.

FIG. 2 illustrates all possible decoding regions that the UE needs toattempt to decode taking into consideration the CCE aggregation level.

The number of all possible decoding regions that a UE needs to attemptto decode according to a CCE aggregation level set in the system may betoo great as can be seen from FIG. 2. Therefore, it is preferable that aregion (a combination of CCE aggregations through which the base stationmay have transmitted a PDCCH to the UE) that the UE needs to attempt todecode be preset for each UE to limit the number of times the UE has todecode in order to receive a PDCCH.

However, the following must be considered when the PDCCH decoding regionis limited. If all different UEs decode the same limited PDCCH decodingregion, the base station must transmit PDCCHs to all UEs only throughthe limited region. Thus, the number of UEs that are simultaneouslycontrollable is restricted since the base station transmits PDCCHs onlythrough the limited region instead of using all available CCEs.

This restriction can be removed if different PDCCH decoding regions (orspaces) are allocated to different UEs. That is, the base station canmore efficiently transmit PDCCHs to a number of UEs as the number of UEswhich do not have an overlapping PDCCH decoding region increases.

FIG. 3 illustrates an example wherein two different UEs have differentdecoding regions under a specific CCE aggregation level condition.

In the following description, a region that each UE needs to attempt todecode to receive a PDCCH is referred to as a “search space”. In theexample of FIG. 3, both a UE 1 and a UE 2 have a CCE aggregation level 1but have different decoding search spaces. That is, the base station cansimultaneously transmit a PDCCH to the UE1 and the UE2 since thedecoding search spaces do not overlap as shown in FIG. 3.

The following methods can be employed to set a different search space toeach UE.

In the first method, a search space having a different start point (orstart position) and a predetermined number of CCEs arranged startingfrom the start point is allocated to each UE so that each UE has adifferent search space.

In the second method, a search space having a different start point anda predetermined number of CCEs arranged at regular intervals startingfrom the start point is allocated to each UE so that each UE has adifferent search space.

These two methods are similar in that the overlapping PDCCH decodingregion can be reduced if the search space of each UE has a differentstart position. Accordingly, an embodiment of the present inventionsuggests that different UE search spaces be set to have different startpositions as described above to minimize overlapping of search spacesthat UEs need to attempt to decode in order to receive a PDCCH. Reducingoverlapping of PDCCH decoding regions in this manner increases thenumber of UEs to which the base station can simultaneously transmitcontrol information through scheduling.

An embodiment of the present invention suggests that a UE identificationnumber that enables identification of each UE from each other be used togenerate a different start position value for each UE as describedabove. It is preferable that as many different values (or numbers) aspossible be generated for UEs. Thus, each generated value will bereferred to as an “identification dependent randomization number”.

FIG. 4 illustrates the principle of a generator that generatesidentification dependent randomization numbers according to anembodiment of the present invention.

Specifically, a generator 401 receives an input value x and generates anoutput value Z_(j) or an output sequence Z according to a generationparameter set {K₀, K₀, . . . K_(L)} of the generator 401. Although thenumber of parameters used in the generator is L+1 in the example of FIG.4, the number and type of the used parameters may vary and will bedescribed in more detail in each embodiment of the present inventiondescribed below.

The value generated by the generator 401 may be a binary sequence or maybe an integer value into which all or part of the binary sequence isconverted.

FIGS. 5 and 6 illustrate an example wherein a part of a binary sequencegenerated by the generator is selected as an initial value according toan embodiment of the present invention.

That is, as shown in FIG. 5, an M-length binary value for use as anidentification dependent randomization number can be selected from aP-length binary sequence generated by the generator 401 described abovewith reference to FIG. 4. According to this embodiment, a number ofidentification dependent randomization numbers can be generated after abinary sequence is generated from a specific initial value. That is, asshown in FIG. 6, partial binary sequences that do not overlap can beselected from the binary sequence generated by the generator 401 and anumber of identification dependent randomization numbers can then begenerated from the selected binary sequences. Although X identificationdependent randomization numbers are generated in the example of FIG. 6,the present invention is not necessarily limited to this example.

When the M-length binary sequence selected for calculating anidentification dependent randomization number is represented by {ŷ₀, ŷ₁,ŷ₂ . . . , ŷ_(M−1)}, this can be used to convert the identificationdependent randomization number (i.e., the start position information)into an integer value Z_(K).

$\begin{matrix}{\mspace{290mu} {{MATHEMATICAL}\mspace{14mu} {EXPRESSION}\mspace{14mu} 1}} & \; \\{{Z_{k} = {{\left( {\sum\limits_{i = 0}^{M - 1}\; {2^{i} \cdot {\hat{y}}_{i}}} \right){mod}\; C\mspace{31mu} Z_{k}} = {\left( {\sum\limits_{i = 0}^{M - 1}\; {2^{M - 1 - i} \cdot {\hat{y}}_{i}}} \right){mod}\; C}}}{OR}{y_{k} \equiv {\sum\limits_{i = 0}^{M - 1}\; {{2^{i} \cdot {\hat{y}}_{i}}\mspace{31mu} y_{k}}} \equiv {\sum\limits_{i = 0}^{M - 1}\; {2^{M - 1 - i} \cdot {\hat{y}}_{i}}}}} & \;\end{matrix}$

Here, it is assumed that a subscript “k” represents a subframe index and“C” is defined as the number of candidate positions that can be used asstart positions. That is, Mathematical Expression 1 represents that aspecific-length binary sequence selected from a binary sequencegenerated by the generator is converted into an integer value and theinteger value is modded with the number of all possible initialpositions “C” to generate a start position value.

Specifically, in an embodiment of the present invention, the value “C”for a PDCCH to be currently received can be set to be equal to a valueobtained by dividing the total number of physical CCEs by a CCEaggregation level (for example, 1, 2, 4, or 8) which is the number ofCCE aggregations that can be used to transmit one PDCCH. If the totalnumber of physical CCEs that can be used for PDCCH transmission isindivisible by the number of CCEs belonging to one PDCCH, the value “C”can be quantized to the number of possible candidate positions based onthe above principle. Specifically, this embodiment suggests that thevalue “C” be obtained using the following equation.

C=floor(N _(CCE) /L _(CCE)),  MATHEMATICAL EXPRESSION 2

where “floor(x)” represents a function to quantize “x” to a largestinteger that is equal to or less than “x”, N_(CCE) represents the totalnumber of CCEs in a specific subframe, and L_(CCE) is the number of CCEsthat are used to transmit one PDCCH.

On the other hand, the generator 401 illustrated in FIG. 4 generatesvalues having a period P. Accordingly, in an embodiment of the presentinvention, it is taken into consideration that P identificationdependent randomization numbers are generated through a value generatedthrough one initial input value. That is, identification dependentrandomization numbers may be generated by performing the binary sequenceselection and integer conversion described above on a binary sequencegenerated through one initialization. Alternatively, a total of Pidentification dependent randomization numbers such as {Z₀, Z₁, Z₂, . .. , Z_(P−1)} may be generated directly from an input initial value.

Communication systems generally operate at preset timings and atintervals of a preset period.

FIG. 7 illustrates a frame structure in the 3GPP LTE system forexplaining an example in which a communication system operates atregular intervals.

Specifically, as shown in FIG. 7, the communication system operates atintervals of a period of “10 ms”. Here, the period “10 ms” can bereferred to as a radio frame. In this system, one radio frame includes10 subframes, each having a length of “1 ms”. Each subframe may have astructure including 0.5 ms slots.

In the example shown in FIG. 7, when randomization effects are achievedusing identification dependent randomization numbers, the generatedvalues may also be handled at intervals of 10 ms since the systemillustrated in FIG. 7 operates at intervals of 10 ms. That is, a systemin which an identification dependent randomization number is requiredfor each subframe may be set to generate a sequence including 10 numbersso that the same sequence is used every period of 10 ms. Alternatively,the system may operate such that a value is generated 10 times everysubframe in a radio frame and values are generated in the same manner ina next radio frame so that the same identification dependentrandomization number is actually generated at intervals of 10 ms.

Reference will now be made to a method in which a start position for usein PDCCH search is generated directly from an initial input value basedon an identification number. In the following, a first embodiment isdescribed as a preferred embodiment of the present invention and secondto fourth embodiments are described as other embodiments that can beimplemented according to a similar principle.

First Embodiment

This embodiment suggests that a value obtained by performing a firstmodulo operation of an input value of “x” with a predetermined constantvalue of “D” and then performing a second modulo operation of theresulting value with a variable value of “C” corresponding to the numberof candidate start positions that can be used as start positions is usedas a search space start position for control information search.

Specifically, this embodiment suggests that a start position bedetermined in the following manner.

Z _(k)=[(A·y _(k) +B)mod D] mod C

y ₀ =x,y _(k)=(A·y _(k−1) +B)mod D

k=0, 1, . . . , P−1  MATHEMATICAL EXPRESSION 3

More specifically, this embodiment suggests that an initial value “x” beinput and then be multiplied by “A” and the sum of the initial value “x”multiplied by “A” and a constant “D” be modded with a variable “C” togenerate a final integer as a start position value of a search space.The finally generated value Z_(k) in Mathematical Expression 3 indicatesa start position of a PDCCH search space in a subframe corresponding toan index “k”.

The following two methods can be used to calculate a search space startposition of a different subframe from the subframe corresponding to theindex “k”.

In the first method, for each subframe, a different initial value isinput to generate a start position value. That is, a different valuesuch as x₀, x₁ . . . x_(k), . . . is sequentially input as an initialvalue for each subframe having an index of k to calculate a startposition Z_(k) of a search space of the subframe. In the second method,an intermediate value generated by inputting an initial value is used asan initial value for the next subframe to generate a start positionvalue. That is, a value of y_(k−1) for a subframe having an index of k−1is used as an input value for a subframe having an index of k.

The above Mathematical Expression 3 according to this embodiment usesthe second method. Specifically, as shown in Mathematical Expression 3,a value obtained by multiplying an intermediate value y_(k−1) by apredetermined constant “A”, adding the intermediate value y_(k−1)multiplied by “A” to a constant “B”, and then modding the resultingvalue with a constant “D” is used as an initial value y_(k).

The value corresponding to the number of candidate start positions “C”as defined in the above Mathematical Expression 2 can also be used inthis embodiment.

In this embodiment, the purpose of performing a modulo operation withthe value “C” defined as in Mathematical Expression 2 is to obtain anoutput value that is one of the candidate start positions. The followingis the reason for performing another modulo operation with “D” beforethe modulo operation with “C” to obtain a value within a desired range.

Even when values of “Ax+B” are different in Mathematical Expression 3,there is high possibility that corresponding final values obtained byperforming a modulo operation of the values “Ax+B” with “C” are likelyto be equal if the value “C” is small. The possibility that differentvalues of “Ax+B” cause collision such that they produce the same finalvalue through the modulo operation with the small value “C” can bereduced by performing another modulo operation with the predeterminedconstant “D”. Here, it is preferable that the predetermined constant “D”be set to be higher than the value “C” to reduce the possibility thatdifferent values of “Ax+B” cause collision as described above.

In this embodiment, it is assumed that the finally obtained search spacestart position Z_(k) in the subframe corresponding to the index “k”indicates a corresponding one of the indices assigned to CCEaggregations corresponding to the CCE aggregation level. That is, whenthe CCE aggregation level is “2”, indices for CCE aggregations areassigned on a 2-CCE basis. Accordingly, the value Z_(k) obtainedaccording to this embodiment indicates a corresponding one of the CCEaggregation indices assigned as described above.

Second Embodiment

Unlike the first embodiment, the finally obtained search space startposition Z_(k) in the subframe corresponding to the index “k” mayindicate a corresponding CCE position based on an index assigned to eachCCE rather than an index assigned to each CCE aggregation. That is, whenthe CCE aggregation level is “2”, a CCE aggregation index may beassigned on a CCE basis rather than on a 2-CCE basis. Accordingly, thisembodiment suggests that a value calculated through the followingequation be used as a start position of a PDCCH search space under thesame condition as in the first embodiment.

Z _(k) =L _(CCE)·[(A·y _(k) +B)mod D] mod C

y ₀ =x,y _(k)=(A·y _(k−1) +B)mod D

k=0, 1, . . . , P−1  MATHEMATICAL EXPRESSION 4

When Mathematical Expression 4 is compared with Mathematical Expression3 according to the first embodiment, it can be seen that a final valueZ_(k) according to Mathematical Expression 4 is obtained by multiplyingthe final value Z_(k) generated according to Mathematical Expression 3by L_(CCE). That is, the value calculated according to MathematicalExpression 3 is multiplied by the number of CCEs L_(CCE) included in oneCCE aggregation according to the CCE aggregation level to generate avalue that can be used as a start position of a search space that isalso appropriate for a system in which indices are assigned on a CCEbasis.

Third Embodiment

In the above Mathematical Expressions 3 and 4, it is assumed that kstarts from “0”. However, the index “k” may also be defined to startfrom “−1”. In this case, Mathematical Expressions 3 and 4 can beexpressed as follows.

Z _(k)=(Y _(k) mod └N _(CCE,k) /L┘)

Y _(k)=(A·Y _(k−1))mod D  MATHEMATICAL EXPRESSION 5

Z _(k) =L·(Y _(k) mod └N _(CCE,k) /L┘)

Y _(k)=(A·Y _(k−1))mod D  MATHEMATICAL EXPRESSION 6

In Mathematical Expressions 5 and 6, it is assumed that Y⁻¹=n_(RNTI)≠0and n_(RNTI) corresponds to a UE ID.

Specifically, Mathematical Expression 5 is equivalent to MathematicalExpression 3 with k starting from −1 and Mathematical Expression 6 isequivalent to Mathematical Expression 4 with k starting from −1.

Fourth Embodiment

This embodiment suggests a second method for calculating a startposition of a PDCCH search space in which the following equation is usedunlike those used in the first to third embodiments.

Z _(k)=((A·x _(k) +B·x _(k) ²)mod D)mod C  MATHEMATICAL EXPRESSION 7

That is, this embodiment suggests that a start position value begenerated using a quadratic generation equation as shown in MathematicalExpression 7 as an input value. Here, the input value may be used inboth the method in which a new value is input for each generation of asubframe value and the method in which a value generated in a kthgeneration is used as an input value for a k+1th generation.

On the other hand, a preferred embodiment of the present inventionsuggests that a number, which is 1 greater than the largest number thatthe initial value may have, (i.e., a value indicating the range ofnumbers that the initial value may have) be used as the value “D” inMathematical Expression 7.

In the above embodiments, it is assumed that UE identificationinformation is used as the initial input value. However, another aspectof the present invention suggests that the initial input value be usedin various forms to enable efficient PDCCH transmission and detection.

The basic purpose of each embodiment of the present invention is togenerate a different value for any specific identification number, whichwill also be referred to as an “ID” for short, and thus it is preferableto select an initial value which maximizes randomization effectsaccording to the ID.

Since the purpose of each embodiment of the present invention is toimpart randomization effects of PDCCH decoding regions between UEs and abase station and it is not necessary to take into considerationrandomization effects between base stations, ID values for identifyingUEs such as UE identification numbers (for example, a C-RTNI or atemporary-RNTI) can be selected as initial values. Specifically, all ofthe following information items or combinations thereof can be used tocreate initial values.

1. UE ID

2. CCE aggregation Level (L_(CCE))

3. Subframe Number (or Slot Number)

According to the present invention, when a sequence is generated as anID dependent random number synchronously with the timings of radioframes, both the method in which a start position value is generatedusing a different initial value every subframe, and the method in whicha start position value is generated synchronously with the timings ofradio frames and a new ID dependent random number is then generatedusing the generated start position value or the intermediate value, maybe employed as described above.

In the method in which an initial value is input every subframe togenerate an ID dependent random number every subframe, the initial valuemust be changed every subframe and a different value must be generatedfor each UE and therefore an initial value may be created using a UE IDand a subframe number (or a corresponding slot number). It is preferablethat the initial value be created such that a number indicating the UEID and a number indicating the subframe not overlap when the initialvalue is expressed in binary form.

FIGS. 8 and 9 illustrate a method for creating an initial value used togenerate a start position of a PDCCH search space using a UE ID and asubframe number according to an embodiment of the present invention.

Specifically, as shown in FIG. 8, when the initial value is expressed inbinary form, the initial value can be created such that a 16-bit UE IDis placed at less significant bit positions including a LeastSignificant Bit (LSB) position of the binary value and a 4-bit subframenumber is placed at more significant bit positions including a MostSignificant Bit (MSB) position. The initial value created in this mannercan be expressed as follows.

{UE−ID}×2⁰+{subframe#}×2¹⁶  MATHEMATICAL EXPRESSION 8

In addition, as shown in FIG. 9, when the initial value is expressed inbinary form, the initial value can be created such that a UE ID isplaced at more significant bit positions including a Most SignificantBit (MSB) position of the binary value and a subframe number is placedat less significant bit positions including a Least Significant Bit(LSB) position. In this case, the initial value can be expressed asfollows.

{UE−ID}×2⁴+{subframe#}×2⁰  MATHEMATICAL EXPRESSION 9

It is preferable that, when a PDCCH decoding region is randomized,randomization effects of each CCE aggregation level be different sincethe same physical CCE may be used even when different CCE aggregationlevels are employed.

FIG. 10 illustrates an example wherein one of two UEs having differentCCE aggregation levels fails to receive a PDCCH destined for the UE dueto a PDCCH destined for the other UE.

A problem may occur if the CCE region for PDCCH decoding is the same forall UEs even though their CCE aggregation levels are different. Forexample, if a PDCCH decoding region corresponding to 8 aggregated CCEsfor transmitting a PDCCH to a UE1 must also be used for a UE 2 when thePDCCH is transmitted to the UE 1 using the CCE aggregation of 8 CCEs, aPDCCH may not be able to be transmitted to the UE 2 since a PDCCHdecoding region for transmission to the UE2 is entirely covered by thePDCCH that uses the 8 aggregated CCEs.

To overcome this problem, an embodiment of the present inventionsuggests that a different identification dependent randomization numberbe generated for each CCE aggregation level. Specifically, theembodiment of the present invention suggests that information of eachCCE aggregation level be incorporated into an initial value used tocalculate a start position of a PDCCH search space. That is, a UE ID, asubframe number, and a CCE aggregation level may be used to create theinitial value.

FIGS. 11 and 12 illustrate examples where a UE ID, a subframe number,and a CCE aggregation level are used to create an initial valueaccording to an embodiment of the present invention.

Specifically, FIG. 11 illustrates an example wherein the initial valueincludes a subframe number, a CCE aggregation level, and a UE ID at bitpositions sequentially from the MSB to the LSB positions and FIG. 12illustrates an example wherein the initial value includes a UE ID, a CCEaggregation level, and a subframe number at bit positions sequentiallyfrom the MSB to the LSB positions. These information items may bearranged in any other order, provided that the initial value includesall the information items.

Alternatively, when the initial value generation methods of the first tofifth embodiments described above are used, an initial value includingno subframe number may be input to generate sequences synchronously withthe timings of radio frames and sequence values generated in eachsubframe may then be used one by one. In this case, the initial valuecan be created using a combination of the UE ID and the CCE aggregationlevel information since there is no need to incorporate the subframeinformation into the initial value.

FIGS. 13 and 14 illustrate examples where an initial value used tocalculate a start position of a PDCCH search space is created using a UEID and a CCE aggregation level according to an embodiment of the presentinvention.

Although the initial value includes a CCE aggregation level and a UE IDat bit positions sequentially from the MSB to the LSB in the example ofFIG. 13 and the initial value includes a CCE aggregation level and a UEID at bit positions in the reverse order in the example of FIG. 14, theCCE aggregation level and the UE ID may be arranged in any order.

On the other hand, another embodiment of the present invention suggeststhat each of the constant values A, B, and D used in the first to fifthembodiments vary depending on the CCE aggregation level. Although thevalue C is represented by a function of the CCE aggregation level andthus varies according to circumstances, the values A, B, and D areconstants preset at transmitting and receiving sides. However, in orderto generate a different identification dependent randomization numberpattern for each CCE aggregation level, the values A, B, and D may eachbe set to be different for each CCE aggregation level.

In a special embodiment, constant values, which are fixed regardless ofthe CCE aggregation level, may be used as the values A and D used in thefirst to fourth embodiments while only the value B is defined to bedifferent for each CCE aggregation level. This allows a finally obtainedsequence to be different for each CCE aggregation level withoutsignificantly changing the characteristics of the generated sequence.

Another possible method is to use only the UE ID as an initial valuewhile especially using fixed, constant values as the values A, B, and Din the first to fifth embodiments since the value C inherently variesaccording to the CCE aggregation level. It is not necessary to definevalues A, B, and D that vary according to the CCE aggregation level inthe above embodiments since a value randomized to some extent isgenerated through a modulo operation with the value D and the finallyobtained identification dependent random number may vary through themodulo operation with the value C that varies according to the CCEaggregation level.

Reference will now be made in detail to parameter values of thegeneration equations for obtaining a start position of a PDCCH searchspace according to the first to fifth embodiments described above.

Using a computer, the present inventor found some values of theparameters A, B, and D of the generator which are good for each method.The good values are defined as follows and the present inventionsuggests best parameter values for each search criterion describedbelow.

A start position of a PDCCH decoding region for decoding for each CCEaggregation level is obtained based on an identification dependentrandomization number. The PDCCH decoding region should be synchronizedbetween the base station and UEs and the period and timing of generationof an identification dependent randomization number should also besynchronized between all UEs that communicate with the base station.Thus, overlapping of PDCCH decoding regions can be minimized ifidentification dependent randomization numbers that UEs having differentUE IDs use every subframe are different. This indicates that, eventhough some identification dependent randomization numbers are equalamong identification dependent randomization numbers generated withdifferent UE IDs, randomization effects can be achieved if theidentification dependent randomization numbers are different only in asubframe in which a specific value is used.

In an embodiment of the present invention, a concept of the “number ofhits” is defined as a criterion for determining performance according toeach parameter value. Each of the UEs having different UE IDs generatesidentification dependent randomization numbers synchronously with radioframes and compares identification dependent randomization numbers usedin subframes to determine the number of subframes which has used thesame value and records the determined number of subframes as the “numberof hits”. Therefore, a distribution of the numbers of hits with allother possible UE IDs is measured for every UE ID that can be allocatedand the distribution of the numbers of hits probabilistically determinedwhen a specific generation method is used is set as one criterion fordetermining performance.

FIG. 15 illustrates the concept of the number of hits used fordetermining performance when parameter values are calculated accordingto an embodiment of the present invention.

That is, the embodiment of the present invention suggests that, since 10subframes are included in a radio frame in the 3GPP LTE as shown in FIG.15, the number of possible hits be determined for subframe indices of 0,1, . . . , 10 and the determined number of hits be used as a probabilitythat UEs having two different UE IDs use the same PDCCH decoding region(i.e., as a criterion for determining performance).

On the other hand, an embodiment of the present invention suggests thata distribution map of an identification dependent randomizationnumber(s) that can be generated from all input initial values that canbe generated according to the generation method with specific parametersA, B, and D be taken into consideration as a second criterion fordetermining performance. Identification dependent randomization numbersgenerated using all generation methods suggested in the presentinvention are between 0 to C−1. Therefore, the embodiment of the presentinvention suggests that a distribution of integer values between 0 toC−1 generated for all initial values that can be input be measured andwhether or not all generated values are as uniform as possible then bedetermined and the uniformity of the generated values then be used as acriterion for determining performance.

In this embodiment, the following performance indicators are selectedfrom performance results. When specific parameters are used in eachgeneration method, the following indicators are calculated and compared.Here, the average of values measured when the value C varies in a rangefrom 96 to 3 is determined for each of the indicators.

1. Maximum number of hits

2. Average number of hits

3. Whether or not ID dependent randomization numbers have been generateduniformly in a range of 0 to C−1

4. Variance of probabilities that values between 0 to C−1 will begenerated for determining whether or not ID dependent randomizationnumbers have been generated uniformly in a range of 0 to C−1

First, parameter values used in the method for generating a startposition of a PDCCH search space according to the first embodiment aredescribed below with reference to the above description.

Various values can be used as constant values A, B, and D that arepredetermined and used at the transmitting and receiving sides in thegeneration method according to the first embodiment. Thus, it isdifficult to measure performance of all possible values of A, B, and Dusing a computer. Therefore, values of A, B, and D that generallyexhibited high performance were first confirmed using a computer andrespective performance of specific combinations of A, B, and D wascompared based on the confirmed values.

First, results of performance measurement using a computer showed thatthe value D exhibited highest performance when similar to the maximumvalue that can be expressed by the initial value x with A and B fixed tospecific values. Results shown in Table 2 are part of performancemeasurement results indicating the probability that sequences generatedfor different UE IDs using an initial value created using only the UEIDs according to the first embodiment become equal in each subframe. TheUE ID consists of 16 bits that correspond to 65536 (=2¹⁶) values.

TABLE 2 Parameters Probability per Number of Hits A B C D 0 1 2 3 4 5 67 8 9 10 4093 7 96 65536 96.931% 0.270% 0.613% 0.811% 0.705% 0.431%0.183% 0.048% 0.007% 0.000% 0.000% 4093 7 86 65536 89.560% 9.404% 0.926%0.088% 0.021% 0.002% 0.000% 0.000% 0.000% 0.000% 0.000% 4093 7 76 6553689.585% 8.162% 1.876% 0.297% 0.062% 0.017% 0.001% 0.000% 0.000% 0.000%0.000% 4093 7 66 65536 86.717% 11.644% 1.464% 0.142% 0.029% 0.005%0.000% 0.000% 0.000% 0.000% 0.000% 4093 7 56 65536 90.213% 4.439% 3.376%1.422% 0.404% 0.110% 0.031% 0.005% 0.000% 0.000% 0.000% 4093 7 46 6553681.970% 14.810% 2.822% 0.333% 0.053% 0.012% 0.000% 0.000% 0.000% 0.000%0.000% 4093 7 36 65536 82.624% 9.787% 5.402% 1.699% 0.384% 0.086% 0.018%0.001% 0.000% 0.000% 0.000% 4093 7 26 65536 72.397% 18.821% 7.045%1.460% 0.234% 0.039% 0.004% 0.000% 0.000% 0.000% 0.000% 4093 7 16 6553693.751% 0.000% 0.000% 0.000% 0.000% 0.000% 0.000% 0.000% 0.000% 0.000%6.249% 4093 7 6 65536 50.867% 4.337% 9.753% 13.006% 11.379% 6.833%2.844% 0.812% 0.152% 0.015% 0.001% 4093 7 96 65537 90.078% 9.459% 0.444%0.018% 0.000% 0.000% 0.000% 0.000% 0.000% 0.000% 0.000% 4093 7 86 6553788.977% 10.457% 0.542% 0.024% 0.000% 0.000% 0.000% 0.000% 0.000% 0.000%0.000% 4093 7 76 65537 87.601% 11.686% 0.681% 0.031% 0.000% 0.000%0.000% 0.000% 0.000% 0.000% 0.000% 4093 7 66 65537 85.830% 13.248%0.879% 0.043% 0.000% 0.000% 0.000% 0.000% 0.000% 0.000% 0.000% 4093 7 5665537 83.471% 15.281% 1.182% 0.065% 0.001% 0.000% 0.000% 0.000% 0.000%0.000% 0.000% 4093 7 46 65537 80.216% 17.964% 1.705% 0.112% 0.004%0.000% 0.000% 0.000% 0.000% 0.000% 0.000% 4093 7 36 65537 75.410%21.668% 2.684% 0.225% 0.013% 0.000% 0.000% 0.000% 0.000% 0.000% 0.000%4093 7 26 65537 67.471% 27.239% 4.709% 0.536% 0.045% 0.000% 0.000%0.000% 0.000% 0.000% 0.000% 4093 7 16 65537 52.355% 35.182% 10.360%1.846% 0.241% 0.016% 0.001% 0.000% 0.000% 0.000% 0.000% 4093 7 6 6553716.152% 32.305% 29.049% 15.530% 5.421% 1.303% 0.216% 0.022% 0.001%0.000% 0.000% 4093 7 96 131071 90.052% 9.500% 0.443% 0.005% 0.000%0.000% 0.000% 0.000% 0.000% 0.000% 0.000% 4093 7 86 131071 88.956%10.484% 0.552% 0.008% 0.000% 0.000% 0.000% 0.000% 0.000% 0.000% 0.000%4093 7 76 131071 87.603% 11.667% 0.714% 0.015% 0.001% 0.000% 0.000%0.000% 0.000% 0.000% 0.000% 4093 7 66 131071 85.869% 13.150% 0.959%0.022% 0.001% 0.000% 0.000% 0.000% 0.000% 0.000% 0.000% 4093 7 56 13107183.506% 15.186% 1.268% 0.039% 0.001% 0.000% 0.000% 0.000% 0.000% 0.000%0.000% 4093 7 46 131071 80.272% 17.820% 1.822% 0.082% 0.003% 0.000%0.000% 0.000% 0.000% 0.000% 0.000% 4093 7 36 131071 75.448% 21.532%2.839% 0.173% 0.008% 0.000% 0.000% 0.000% 0.000% 0.000% 0.000% 4093 7 26131071 67.563% 26.983% 4.938% 0.478% 0.035% 0.002% 0.000% 0.000% 0.000%0.000% 0.000% 4093 7 16 131071 52.421% 34.996% 10.518% 1.826% 0.218%0.020% 0.001% 0.000% 0.000% 0.000% 0.000% 4093 7 6 131071 16.152%32.303% 29.064% 15.505% 5.436% 1.305% 0.212% 0.022% 0.001% 0.000% 0.000%4093 7 96 1048576 96.933% 0.273% 0.608% 0.810% 0.705% 0.423% 0.181%0.056% 0.011% 0.001% 0.000% 4093 7 86 1048576 89.526% 9.415% 0.980%0.075% 0.004% 0.000% 0.000% 0.000% 0.000% 0.000% 0.000% 4093 7 761048576 89.539% 8.158% 1.963% 0.305% 0.032% 0.003% 0.000% 0.000% 0.000%0.000% 0.000% 4093 7 66 1048576 86.711% 11.603% 1.538% 0.135% 0.011%0.001% 0.000% 0.000% 0.000% 0.000% 0.000% 4093 7 56 1048576 90.226%4.407% 3.331% 1.485% 0.448% 0.088% 0.013% 0.001% 0.000% 0.000% 0.000%4093 7 46 1048576 81.991% 14.739% 2.868% 0.363% 0.037% 0.002% 0.000%0.000% 0.000% 0.000% 0.000% 4093 7 36 1048576 82.819% 9.543% 5.299%1.831% 0.420% 0.076% 0.011% 0.000% 0.000% 0.000% 0.000% 4093 7 261048576 72.450% 18.720% 7.031% 1.552% 0.226% 0.020% 0.000% 0.000% 0.000%0.000% 0.000% 4093 7 16 1048576 93.751% 0.000% 0.000% 0.000% 0.000%0.000% 0.000% 0.000% 0.000% 0.000% 6.249% 4093 7 6 1048576 50.873%4.339% 9.758% 12.995% 11.371% 6.828% 2.852% 0.815% 0.152% 0.016% 0.001%4093 7 96 1048593 90.946% 7.811% 1.145% 0.089% 0.007% 0.001% 0.000%0.000% 0.000% 0.000% 0.000% 4093 7 86 1048593 89.008% 10.392% 0.580%0.020% 0.000% 0.000% 0.000% 0.000% 0.000% 0.000% 0.000% 4093 7 761048593 87.581% 11.711% 0.690% 0.017% 0.000% 0.000% 0.000% 0.000% 0.000%0.000% 0.000% 4093 7 66 1048593 87.595% 9.980% 2.141% 0.265% 0.019%0.001% 0.000% 0.000% 0.000% 0.000% 0.000% 4093 7 56 1048593 89.444%5.445% 3.401% 1.315% 0.333% 0.055% 0.006% 0.001% 0.000% 0.000% 0.000%4093 7 46 1048593 95.658% 0.043% 0.191% 0.509% 0.891% 1.070% 0.892%0.510% 0.190% 0.041% 0.004% 4093 7 36 1048593 80.612% 12.724% 5.202%1.240% 0.198% 0.021% 0.002% 0.001% 0.000% 0.000% 0.000% 4093 7 261048593 92.317% 0.074% 0.337% 0.903% 1.578% 1.892% 1.578% 0.902% 0.338%0.075% 0.007% 4093 7 16 1048593 52.396% 35.073% 10.456% 1.826% 0.225%0.022% 0.002% 0.000% 0.000% 0.000% 0.000% 4093 7 6 1048593 66.700%0.325% 1.465% 3.905% 6.836% 8.206% 6.836% 3.904% 1.465% 0.325% 0.032%4093 7 96 2097143 90.048% 9.514% 0.425% 0.012% 0.000% 0.000% 0.000%0.000% 0.000% 0.000% 0.000% 4093 7 86 2097143 88.997% 10.412% 0.572%0.019% 0.000% 0.000% 0.000% 0.000% 0.000% 0.000% 0.000% 4093 7 762097143 87.614% 11.655% 0.704% 0.027% 0.000% 0.000% 0.000% 0.000% 0.000%0.000% 0.000% 4093 7 66 2097143 85.845% 13.210% 0.911% 0.034% 0.001%0.000% 0.000% 0.000% 0.000% 0.000% 0.000% 4093 7 56 2097143 83.487%15.250% 1.200% 0.063% 0.001% 0.000% 0.000% 0.000% 0.000% 0.000% 0.000%4093 7 46 2097143 80.294% 17.816% 1.765% 0.120% 0.005% 0.000% 0.000%0.000% 0.000% 0.000% 0.000% 4093 7 36 2097143 75.434% 21.612% 2.724%0.217% 0.013% 0.000% 0.000% 0.000% 0.000% 0.000% 0.000% 4093 7 262097143 67.573% 26.986% 4.897% 0.512% 0.031% 0.001% 0.000% 0.000% 0.000%0.000% 0.000% 4093 7 16 2097143 52.462% 34.907% 10.552% 1.859% 0.206%0.014% 0.000% 0.000% 0.000% 0.000% 0.000% 4093 7 6 2097143 16.176%32.240% 29.086% 15.553% 5.420% 1.280% 0.216% 0.027% 0.002% 0.000% 0.000%As shown in Table 2, the probability that collision occurs (i.e., UE IDsbecome equal) in all of the 10 subframes is 6.429% when the value D isequal to an initial value of 2¹⁶ and the value C is 16. However, thisphenomenon disappears when the value D is greater than 2¹⁶. It can beseen from Table 2 that the phenomenon disappears when the value D is65537 or 131071 which are greater than 2¹⁶. However, such poorperformance results occur when a value much greater than 2¹⁶ is selectedas the value D. That is, such results occur when the value D is 1048576or 1048593. Although performance is increased when the value D is2097143, the performance is, on average, lower than that when a valuewhich is close to 2¹⁶ and greater than 2¹⁶ is used as the value D.

Based on these facts, an embodiment of the present invention suggeststhat a prime number greater than 2^(N) and less than 2^(N+1) be used asthe parameter value D when the initial value is expressed by N bits.Preferably, the smallest prime number greater than 2^(N) is used as theparameter value D. Specifically, an embodiment suggests that a value of2¹⁶+1 be used as the value D when N=16, a value of 2¹⁸+3 be used as thevalue D when N=18, and a value of 2²²+15 be used as the value D whenN=22. The reason why this embodiment suggests that the smallest primenumber that satisfies performance requirements be used as the value D isthat the simplicity of phenomenon increases, approaching that of normalphenomena, as the value D decreases.

Consequently, an embodiment of the present invention suggests that avalue of 65537 be used as the parameter D of the start positiongeneration equation according to the first embodiment of the presentinvention when it is assumed that the initial value for the generationequation is generated based on a 16-bit UE ID.

On the other hand, to select a parameter value of B, performance wasmeasured using various values of A and various values of B with thevalue D being fixed to a specific value. Such measurement results showedthat the parameter B has no significant influence on the variance of theprobabilistic distribution of generation of each value of between 0 andC−1, the average number of collisions, and the maximum number ofcollisions when the parameters D and A are prime. The following Table 3shows part of the various performance measurement results.

TABLE 3 Variance of probability of generation for each Maximum numberbetween 0 and Average number number A B D c-1 of Hits of hits 32789 01048567 8.29439756700E−04 1.31635866660E+00 6 32789 7 10485678.29439750350E−04 1.31635868060E+00 6 32789 3821 10485678.29439765480E−04 1.31635878580E+00 6 33037 0 1048567 8.29439348280E−041.31635500230E+00 7 33037 7 1048567 8.29439329360E−04 1.31635487980E+007 33037 3821 1048567 8.29439315490E−04 1.31635479360E+00 7 34421 01048567 8.29439612880E−04 1.31635698230E+00 10 34421 7 10485678.29439589840E−04 1.31635668660E+00 10 34421 3821 10485678.29439602550E−04 1.31635693940E+00 10 36061 0 1048567 8.29439625390E−041.31635759420E+00 8 36061 7 1048567 8.29439596140E−04 1.31635773990E+008 36061 3821 1048567 8.29439654740E−04 1.31635777670E+00 8 41189 01048567 8.29441337570E−04 1.31637294490E+00 6 41189 7 10485678.29441321130E−04 1.31637275310E+00 6 41189 3821 10485678.29441026210E−04 1.31637274940E+00 6 43789 0 1048567 8.29675510000E−041.31860997820E+00 7 43789 7 1048567 8.29674822710E−04 1.31859473170E+007 43789 3821 1048567 8.29673565670E−04 1.31860202780E+00 7 47653 01048567 8.29440200970E−04 1.31636344580E+00 8 47653 7 10485678.29440320540E−04 1.31636344670E+00 8 47653 3821 10485678.29440282120E−04 1.31636322130E+00 8

Therefore, an embodiment of the present invention suggests that theparameter values D and A be set to be prime and the parameter value B beset to a very small integer or 0. The complexity of calculation can bereduced when the value B is 0 or approaches 0.

Consequently, a preferred embodiment of the present invention suggeststhat the parameter value B be set to “0” in the generation equation ofthe first embodiment.

On the other hand, to select a parameter value A, performance wasmeasured using an available prime number less than the value D whilefixing the value B, which is determined to have no significant influenceon performance, to a specific value and fixing the value D to a valuethat exhibited high performance according to the initial value. Thefollowing Table 4 shows part of such performance measurement results.

TABLE 4 Variance of Maxi- probability mum of genera- num- tion for eachber number Average number of A B D between 0 and c-1 of Hits hits 398277 65537 8.29439188640E−04 1.31635211090E+00 6 34231 7 655378.29439188930E−04 1.31635211140E+00 6 46889 7 65537 8.29439189470E−041.31635211190E+00 6 52289 7 65537 8.29439190000E−04 1.31635211190E+00 655717 7 65537 8.29439189710E−04 1.31635211190E+00 6 53831 7 655378.29439189320E−04 1.31635211190E+00 6 32993 7 65537 8.29439189850E−041.31635211230E+00 6 50923 7 65537 8.29439190530E−04 1.31635211280E+00 656131 7 65537 8.29439190290E−04 1.31635211280E+00 6 60889 7 655378.29439190530E−04 1.31635211280E+00 6 63601 7 65537 8.29439190390E−041.31635211280E+00 6 53437 7 65537 8.29439190780E−04 1.31635211280E+00 640151 7 65537 8.29439190530E−04 1.31635211280E+00 6 46831 7 655378.29439190190E−04 1.31635211280E+00 6 36011 7 65537 8.29439190820E−041.31635211330E+00 6 64747 7 65537 8.29439190630E−04 1.31635211330E+00 639041 7 65537 8.29439190680E−04 1.31635211330E+00 6 47609 7 655378.29439190820E−04 1.31635211330E+00 6 34501 7 65537 8.29439191160E−041.31635211330E+00 6 36821 7 65537 8.29439190820E−04 1.31635211330E+00 642061 7 65537 8.29439191210E−04 1.31635211330E+00 6 34703 7 655378.29439190820E−04 1.31635211330E+00 6 35863 7 65537 8.29439190730E−041.31635211330E+00 6 47639 7 65537 8.29439190870E−04 1.31635211330E+00 651767 7 65537 8.29439190820E−04 1.31635211330E+00 6 40627 7 655378.29439191450E−04 1.31635211370E+00 6 40883 7 65537 8.29439191450E−041.31635211370E+00 6 41011 7 65537 8.29439191160E−04 1.31635211370E+00 644483 7 65537 8.29439191310E−04 1.31635211370E+00 6 45179 7 655378.29439191120E−04 1.31635211370E+00 6 45523 7 65537 8.29439191210E−041.31635211370E+00 6 58043 7 65537 8.29439191160E−04 1.31635211370E+00 659083 7 65537 8.29439191450E−04 1.31635211370E+00 6 64499 7 655378.29439191410E−04 1.31635211370E+00 6 41521 7 65537 8.29439191210E−041.31635211370E+00 6 42281 7 65537 8.29439191310E−04 1.31635211370E+00 643577 7 65537 8.29439191210E−04 1.31635211370E+00 6 45737 7 655378.29439191450E−04 1.31635211370E+00 6 49481 7 65537 8.29439191500E−041.31635211370E+00 6 57041 7 65537 8.29439191450E−04 1.31635211370E+00 634877 7 65537 8.29439191410E−04 1.31635211370E+00 6 41957 7 655378.29439191210E−04 1.31635211370E+00 6 45389 7 65537 8.29439191410E−041.31635211370E+00 6 61861 7 65537 8.29439191500E−04 1.31635211370E+00 6. . . . . . . . . . . . . . . . . . 51977 7 65537 8.29439195530E−041.31635211740E+00 9 61441 7 65537 8.29439193350E−04 1.31635211510E+00 964513 7 65537 8.29439196010E−04 1.31635211790E+00 9 65521 7 655378.29439192330E−04 1.31635211370E+00 9 34607 7 65537 8.29439192670E−041.31635211510E+00 9 53239 7 65537 8.29439196260E−04 1.31635211840E+00 963863 7 65537 8.29439194270E−04 1.31635211650E+00 9

In Table 4, values of “A” exhibiting the smallest numbers of collisionsare first arranged and remaining values are arranged in decreasing orderof the average number of collisions. That is, the value of A located atan upper portion of Table 4 exhibits high performance in terms ofperformance indicators. Thus, an embodiment of the present inventionsuggests that one of the values written above symbols “ . . . ” in Table4 be used as the value A. Particularly, a preferred embodiment of thepresent invention suggests that a value of 39827 written at the top ofTable 4 be used as the value A.

Consequently, a preferred embodiment of the present invention suggeststhat values of 39827, 0, and 65537 be used respectively as the parametervalues A, B, and D of the generation equation according to the firstembodiment of the present invention. However, when it is necessary touse other parameter values according to system requirements, valuesselected from those written in the following table can be used as theparameter values A, B, and D.

TABLE 5 A B D 39827, 34231, 46889, 0, 1, 3, 5, 7 2¹⁶ + 1, 2¹⁸ + 3, 2²⁰ +7, 2²² + 15, 52289

The equations for calculating a start position of a PDCCH search spaceaccording to the second to fourth embodiments are substantiallyidentical to that of the first embodiment in terms of their meanings.Accordingly, the present invention suggests that values of 39827, 0, and65537 also be used respectively as the parameter values A, B, and D inthe second to fourth embodiments. In this case, values written in Table5 can be used as the parameter values A, B, and D when it is necessaryto use parameter values other than 39827, 0, and 65537 according tosystem requirements.

The parameters of the generation equation used in the fifth embodimentof the present invention can also be determined in a manner similar tothe method described above. The present inventor also measured variousperformance criteria for the parameters of the generation equation ofthe fifth embodiment and suggests that the following combinations ofparameters be used.

TABLE 6 A B D 7 16 2²⁰ 15 32 2²⁰ 31 64 2²⁰

The detailed description of the preferred embodiments of the presentinvention has been given to enable those skilled in the art to implementand practice the invention. Although the invention has been describedwith reference to the preferred embodiments, those skilled in the artwill appreciate that various modifications and variations can be made inthe present invention without departing from the spirit or scope of theinvention described in the appended claims.

Accordingly, the invention should not be limited to the specificembodiments described herein, but should be accorded the broadest scopeconsistent with the principles and novel features disclosed herein.

The above embodiments can be applied not only to the 3GPP LTE system butalso to various other systems that need to transmit a downlink controlchannel to each UE.

1. A method for decoding control information by a User Equipment (UE),the method comprising: receiving a Physical Downlink Control Channel(PDCCH) from a base station at subframe k; and decoding a set of PDCCHcandidates comprising ‘L’ control channel elements (CCEs) within asearch space of the PDCCH at the subframe k, wherein the ‘L’ CCEscorresponding to a specific PDCCH candidate among the set of PDCCHcandidates of the search space at the subframe k are contiguouslylocated from a position given by using a variable of Y_(k) for thesubframe k and a modulo operation based on ‘floor(N/L)’, wherein ‘N’represent a total number of CCEs in the subframe k, and wherein Y_(k) isdefined by:Y _(k)=(A*Y _(k−1))mod D, wherein A, and D are predetermined constantvalues.
 2. The method of claim 1, wherein A and D are 39827 and 65537,respectively.
 3. The method of claim 1, wherein ‘L’ is one of 1, 2, 4and
 8. 4. The method of claim 1, wherein the ‘L’ CCEs corresponding to afirst PDCCH candidate among the set of PDCCH candidates of the searchspace at the subframe k are contiguously located from a position givenby:L*{(Y_(k))mod(floor(N/L))}.
 5. The method of claim 1, wherein the ‘L’CCEs corresponding to a first PDCCH candidate among the set of PDCCHcandidates of the search space at the subframe k are located atpositions given by:L*{(Y _(k))mod(floor(N/L))}+i, wherein i=0, . . . , L−1.
 6. A userequipment (UE) for decoding control information, the UE comprising: areceiver for receiving a Physical Downlink Control Channel (PDCCH) froma base station at subframe k; and a decoder for decoding a set of PDCCHcandidates comprising ‘L’ control channel elements (CCEs) within asearch space of the PDCCH at the subframe k, wherein the ‘L’ CCEscorresponding to a specific PDCCH candidate among the set of PDCCHcandidates of the search space at the subframe k are contiguouslylocated from a position given by using a variable of Y_(k) for thesubframe k and a modulo operation based on ‘floor(N/L)’, wherein ‘N’represent a total number of CCEs in the subframe k, and wherein Y_(k) isdefined by:Y _(k)=(A*Y _(k−1))mod D, wherein A, and D are predetermined constantvalues.
 7. The UE of claim 6, wherein A and D are 39827 and 65537,respectively.
 8. The UE of claim 6, wherein ‘L’ is one of 1, 2, 4 and 8.9. The UE of claim 6, wherein the ‘L’ CCEs corresponding to a firstPDCCH candidate among the set of PDCCH candidates of the search space atthe subframe k are contiguously located from a position given by:L*{(Y_(k))mod(floor(N/L))}.
 10. The UE of claim 6, wherein the ‘L’ CCEscorresponding to a first PDCCH candidate among the set of PDCCHcandidates of the search space at the subframe k are located atpositions given by:L*{(Y _(k))mod(floor(N/L))}+i, wherein i=0, . . . , L−1.
 11. A methodfor transmitting control information by a base station, the methodcomprising: transmitting a Physical Downlink Control Channel (PDCCH) toa user equipment (UE) at subframe k, wherein the PDCCH comprises a setof PDCCH candidates, wherein the set of PDCCH candidates comprising ‘L’control channel elements (CCEs) within a search space of the PDCCH atthe subframe k, wherein the ‘L’ CCEs corresponding to a specific PDCCHcandidate among the set of PDCCH candidates of the search space at thesubframe k are contiguously located from a position given by using avariable of Y_(k) for the subframe k and a modulo operation based on‘floor(N/L)’, wherein ‘N’ represent a total number of CCEs in thesubframe k, and wherein Y_(k) is defined by:Y _(k)=(A*Y _(k−1))mod D, wherein A, and D are predetermined constantvalues.
 12. The method of claim 11, wherein A and D are 39827 and 65537,respectively.
 13. The method of claim 11, wherein ‘L’ is one of 1, 2, 4and
 8. 14. The method of claim 11, wherein the ‘L’ CCEs corresponding toa first PDCCH candidate among the set of PDCCH candidates of the searchspace at the subframe k are contiguously located from a position givenby:L*{(Y_(k))mod(floor(N/L))}.
 15. The method of claim 11, wherein the ‘L’CCEs corresponding to a first PDCCH candidate among the set of PDCCHcandidates of the search space at the subframe k are located atpositions given by:L*{(Y _(k))mod(floor(N/L))}+i, wherein i=0, . . . , L−1.
 16. A basestation for transmitting control information, the base stationcomprising: a transmitter for transmitting a Physical Downlink ControlChannel (PDCCH) to a user equipment (UE) at subframe k, wherein thePDCCH comprises a set of PDCCH candidates, wherein the set of PDCCHcandidates comprising ‘L’ control channel elements (CCEs) within asearch space of the PDCCH at the subframe k, wherein the ‘L’ CCEscorresponding to a specific PDCCH candidate among the set of PDCCHcandidates of the search space at the subframe k are contiguouslylocated from a position given by using a variable of Y_(k) for thesubframe k and a modulo operation based on ‘floor(N/L)’, wherein ‘N’represent a total number of CCEs in the subframe k, and wherein Y_(k) isdefined by:Y _(k)=(A*Y _(k−1))mod D, wherein A, and D are predetermined constantvalues.
 17. The base station of claim 16, wherein A and D are 39827 and65537, respectively.
 18. The base station of claim 16, wherein ‘L’ isone of 1, 2, 4 and
 8. 19. The base station of claim 16, wherein the ‘L’CCEs corresponding to a first PDCCH candidate among the set of PDCCHcandidates of the search space at the subframe k are contiguouslylocated from a position given by:L*{(Y_(k))mod(floor(N/L))}.
 20. The base station of claim 16, whereinthe ‘L’ CCEs corresponding to a first PDCCH candidate among the set ofPDCCH candidates of the search space at the subframe k are located atpositions given by:L*{(Y _(k))mod(floor(N/L))}+i, wherein i=0, . . . , L−1.